1. Field of the Invention
The present invention relates to a method of error correction coding, and a method and apparatus for recording data using the same.
2. Description of the Related Art
Information recording media include magnetic discs such as floppy discs and hard discs, magnetic tapes, semiconductor memory chips such as ROMs and RAMs, and optical discs such as CDs and DVDs.
The recording capacity of an optical disc has rapidly increased along with the development of semiconductor techniques and signal processing techniques, and the price of optical discs is relatively low.
Information recorded on an optical disc is recorded in block units with a predetermined size. The block unit in which data is recorded is also a basic unit for error correction coding (ECC). A size of an ECC block used in a conventional optical disc is generally 32 Kbytes or 64 Kbytes.
Attempts have been made to use the optical disc as an information recording medium for recording and/or reproducing both sound and images simultaneously with a portable electronic device such as a camcorder.
However, the use of the optical disc in such a portable electronic device like a camcorder has a few shortcomings. That is, the size of the optical disc, generally 80 mm or 120 mm, is too big for a camcorder, and power consumption is too high using the conventionally sized optical disc.
Accordingly, to use the optical disc as an information recording medium for a portable electronic device, an optical disc with a smaller size, but higher recording density, than a conventional optical disc is required.
When recording and reproducing data with a conventional size of an ECC block unit on a small-sized optical disc having a diameter of 30-50 mm, a problem may occur in correcting errors when reproducing recorded data.
For error correction coding in a conventional DVD, a Reed-Solomon Production Code (RSPC) is used. In the case of the RSPC, an ECC block unit includes 416 recording frames corresponding to 32 Kbytes of user data. One sync frame includes 1488 channel bits, and one channel bit is 0.133 μm long. Therefore, the length of the unit ECC block in a track direction is 82,328.064 μm, which is equivalent to a circumference of a circle with a radius of 13.1 mm. Accordingly, when the ECC block unit used in the conventional DVD is recorded within a region inside the radius of 13.1 mm, the ECC block unit will occupy more than one track. Therefore, when recording a conventional ECC block unit to a small-sized optical disc having a diameter of 30-50 mm, it is inevitable to record the error correction data on two or more tracks.
FIG. 1 is a schematic drawing showing an inner circumference region of a small-sized optical disc, on which data with a conventional ECC block unit is recorded.
Referring to FIG. 1, when a 64 Kbytes ECC block unit is recorded from an inner circumference region to an outer circumference region in the data recording region within a radius of 6 mm from the center of a small-sized optical disc, the conventional ECC block unit is recorded in the regions from point A to point D. That is, when recording the ECC block unit from the innermost circumference region of the small-sized optical disc, the ECC block unit is recorded on two tracks, thereby generating an overlapping region in a radial direction by the ECC block unit. If there is a scratch in a radial direction on an overlapping region on which the unit ECC block is recorded, a serious error may occur in the ECC block unit, thereby reducing an error correction capability remarkably.
That is, if an ECC block unit is not recorded in only one track, but recorded in two tracks of a small-sized optical disc, the error correction capability of the recorded ECC block unit is remarkably reduced if there is any defect such as a scratch on the inner circumference region.
This problem occurs not only when the RSPC is used as an ECC format, but also occurs when a long distance code (LDC) is used.
According to U.S. Pat. No. 6,367,049, an ECC block unit includes 304 LDCs generated according to RS (248, 216, 33), and 24 burst indicator subcodes (BIS) generated according to RS (62, 32, 33). An ECC block unit includes 64 Kbytes of user data and 496 recording frames. Each recording frame includes a Sync pattern, 152 bytes of ECC data, and 3 bytes of BIS.
When 8 bytes are modulated to 12 bytes according to a modulation method of Run Length Limit (RLL) (1, 7), and if the number of Sync patterns is 20, the length occupied by the ECC block according to the Channel Bit Length (CBL) and ECC format in a track direction is 937,440×CBL.
A length of an ECC block disclosed in U.S. Pat. No. 6,367,049 is equal to a length of the circumference of a circle with a radius of 149,274×CBL. Since error correction corresponding to a length of 64 recording frames is possible according to the ECC format, the maximum error correction length is 120,960×CBL.
Therefore, when the CBL is 0.100 μm, a radius of a circle having a circumference equal to the length of the ECC block is 14.93 mm, and the maximum error correction length is about 12.10 mm.
When the CBL is 0.090 μm, a radius of a circle having a circumference equal to the length of the ECC block is 13.43 mm, and the maximum error correction length is about 10.89 mm.
When the CBL is 0.080 μm, a radius of a circle having a circumference equal to the length of the ECC block is 11.94 mm, and the maximum error correction length is about 9.68 mm.
When the CBL is 0.070 μm, a radius of a circle having a circumference equal to the length of the ECC block is 10.45 mm, and the maximum error correction length is about 8.47 mm.
When the CBL is 0.060 μm, a radius of a circle having a circumference equal to the length of the ECC block is 8.96 mm, and the maximum error correction length is about 7.26 mm.
Practically, an optical disc having a diameter of 120 mm does not have an overlapping region for these ECC blocks because the recording commences beyond a radius of 20 mm. However for a small-sized optical disc having a diameter of 30˜50 mm, the radius to commence recording data has to be small to record as much data as possible.
In the case of applying the ECC format of 64 Kbytes disclosed in U.S. Pat. No. 6,367,049 to a small-sized disc in which the recording or storing data commences from a radius of about 6˜9 mm, and when the CBL is larger than 0.060 μm, inevitably the ECC block unit is recorded to two or more tracks.
If the CBL is 0.070 μm, and one recording frame includes 1890 channel bits, a length occupied by the recording frame is 132.3 μm. Accordingly, a 2 mm scratch can affect about 16 consecutive recording frames. In this case, an error of 8 bytes is caused to the RS (248, 216, 33) code, and an error of 16 bytes will be caused when the scratch occurs on an overlapping region on which an ECC block unit is recorded to two tracks.
Assuming that an erase correction is performed on the scratched region and a Byte Error Rate is 10−3, the block error rates (BER) when an 8 bytes error and a 16 bytes error occur in an ECC block unit are shown in Table 1.
TABLE 18 bytes of error16 bytes of errorBER when a scratch is 1 mm7.8 * 10−202.5 * 10−16BER when a scratch is 2 mm2.5 * 10−161.1 * 10−9 
Referring to Table 1, the BER when a scratch occurs on a region in which an ECC block unit is overlapping on two tracks is more than double that of an error when a scratch of the same length occurs on a region in which an ECC block unit is in one track.
A length L of the ECC block unit occupying a length of recording medium in the track direction is a multiple of channel bit numbers CBN of the ECC block, a minimum mark length MML according to a numerical aperture and laser wavelength, and a channel bit length CBL defined by a modulation code. That is, L=CBN×MML×CBL.
At the same modulation code, by increasing the density of recording lines (reducing minimum mark length), and by decreasing the length of the channel bit, the length of the ECC block can be reduced, thereby minimizing or removing a region overlapping two or more tracks by an ECC block unit.
However, an effect of an error causing problem such as a scratch or a finger print is increased in an inversely proportional manner to the reduction of the channel bit length. Consequentially, the effect of an error increases with the reduction of the channel bit length, even though the size of the error causing problem does not change. That is, if the length of the channel bit is reduced, the length of the maximum error correction of the ECC block is also reduced. Therefore, the reduction of the length of channel bit as a way of recovering the error correction capability of the ECC block on an overlapping region accompanies a problem of reducing the maximum error correction length of the ECC block.
Therefore, in a case when reducing the size of the ECC block at a fixed channel bit length (the minimum mark length is equal to the modulation code) and at the same parity ratio, the maximum error correction length may also be reduced. The maximum error correction length under a structure of the ECC format proposed in U.S. Pat. No. 6,367,049 is determined by adding parity of a codeword existing in the ECC block unit to an interleaving depth between codewords. That is, the maximum error correction bytes are 9728 because the ECC format is RS (248, 216, 33) code x 304.
Consequentially, since the size reduction of the ECC block maintaining the parity ratio results in the reduction of an interleaving depth or the reduction of an amount of user data, and adding parity of a codeword, the maximum error correction bytes will be reduced. Accordingly, the reduction of an error correction capability, including a maximum error correction length, will appear.
As described above, when a circumference on a region of the optical disc to which the ECC block is recorded or stored is shorter than the length of the unit ECC block, the unit ECC block is recorded to two or more tracks, thereby reducing the error correction capability, which results in lowering the reproducing reliability.
A conventional optical disc has a structure of recording regions in which a lead-in region, a user data region, and a lead-out region are sequentially formed from an inner circumference region to an outer circumference region. Generally, important information for reproducing data of the optical disc is recorded to the inner circumference region corresponding to the lead-in region.
Therefore, the reduction of error correction capability of the ECC block unit recorded in the inner circumference region becomes a serious problem.